Surface treatment method for carbon steel screws embedded within anticorrosive wood, the associated surface structure and baking finishing formula

ABSTRACT

The surface treatment method for carbon steel screws embedded within anticorrosive wood, the associated surface structure and baking finishing formula are characterized by forming a uniform and fine anticorrosive layer of a baking finishing formula whereby the anticorrosive ability of the surface of a carbon steel screw can be enhanced. The associated baking finishing formula comprise metallic zinc, metallic nickel, metallic aluminum, polyethylene glycol, a silane, fluoride-containing surfactants, corrosion inhibitors and a mixed-type additive.

FIELD OF THE INVENTION

The present invention relates to surface treatments for carbon steel screws and the surface functions thereby produced, more particularly to a surface treatment method for carbon steel screws embedded within anticorrosive wood and the associated baking finishing formula and surface structure, which are characterized by forming a uniform and fine anticorrosive layer of a baking finishing formula whereby the anticorrosive ability of the surface of a carbon steel screw can be enhanced.

BACKGROUND OF THE INVENTION

Wood preservation treatments are needed to resist weather erosion and worm eating. The most common wood preservation treatment is immerses wood in chromated copper arsenate. What we commonly call CCA. However, CCA is potentially hazardous, since children may intake arsenic chromium copper acids by touching outdoor playground facilities through a CCA wood preservation treatment. The prohibition of CCA as a wood preservation method ushers the ACQ method, which is the immersing wood into solution of high copper ion content and using a high pressure to make the copper ions infiltrate into the wooden fibers. The wood thereby produced has a copper ion concentration four times higher than the wood by CCA, which will erode the metallic parts embedded therein badly. Structures made by ACQ wood may collapse after an extended period of time. To reduced the erosion in ACQ wood, the metallic parts in the wood should go through an anticorrosion treatment, which may be one of:

-   1. using metallic parts made of corrosion-resistant alloys; -   2. coating the metallic parts with an impermeable covering; -   3. treating the metallic parts by hot-dip Galvanic coating of zinc.

The screws used in wood structures are made of iron or other non-ironic alloys. The screws made of non-ironic alloys are expensive and too soft. Therefore, the application is limited.

An ironic material after heat treatment by carburizing become a carbon steel material—which is mechanically tough and suitable for making parts associated with ACQ processed wood.

The carbon steel screws embedded within anticorrosive wood have their surfaces commonly plated with zinc by electrolysis and then inactivated by chromic acid. Finally, they will be protected by an organic finishing. They looks beautiful and will not be damaged when they are engaged with the wood. However, the anticorrosive ability of the parts is not satisfactory.

Further, the problem of pollution caused by Chromium-6 in the process of surface inactivation by a chromic acid cannot be ignored.

SUMMARY OF THE INVENTION

Accordingly, the present invention is to provide a surface treatment method for carbon steel screws embedded within anticorrosive wood, the associated surface structure and baking finishing formula whereby a uniform, smooth and fine protective layer of thin film can be formed over a carbon steel screw, and whereby the anticorrosive ability of the surface can be enhanced.

The baking finishing formula for carbon steel screws comprises metallic zinc solution of concentration 5-10 grams per liter and ion particle size 25-75 microns in diameter; metallic nickel solution of concentration 0.2-0.5 grams per liter and ion particle size 100-200 microns in diameter; metallic aluminum solution of concentration 10-20 grams per liter and ion particle size 15-25 microns in diameter; a fluoride-containing surfactant of concentration 0.2% and corresponding to polyethylene glycol; a plurality of corrosion inhibitors in a mixture of succinic anhydride, n-butylamine, n-octylamine, n-decylamine and n-dodecylamine; polyethylene glycol of concentration 30-50 grams per liter and of molecular weight 2000-10000; and a mixed-type additive of concentration 10-60 ppm.

The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photo that shows a collection of carbon steel screws after 90 days of treatment by AWPA E-12 94.

FIG. 2 is another photo that shows another collection of carbon steel screws being processed.

FIG. 3 is a photo that shows a collection of carbon steel screws after 90 days of the treatment of prior art by AWPA E-12 94.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention is a baking formula for carbon steel screws comprising:

-   a. metallic zinc solution of concentration 5-10 grams per liter and     ion particle size 25-75 microns in diameter; -   b. metallic nickel solution of concentration 0.2-0.5 grams per liter     and ion particle size 100-200 microns in diameter; -   c. metallic aluminum solution of concentration 10-20 grams per liter     and ion particle size 15-25 microns in diameter; -   d. a fluoride-containing surfactant of concentration 0.2% and     corresponding to polyethylene glycol; -   e. a plurality of corrosion inhibitors in a mixture of succinic     anhydride, n-butylamine, n-octylamine, n-decylamine and     n-dodecylamine; -   f. polyethylene glycol of concentration 30-50 grams per liter and of     molecular weight 2000-10000; and -   g. a mixed-type additive of concentration 10-60 ppm.

The fluoride-containing surfactant is a product of 3M (Minnesota Mining and Manufacturing Co.) with a product number of FC-4430.

The mixed-type additive is a benzotriazole derivative with the following molecular structure:

The groups R1, R2, R3 and R4 are selected from alkyls of carbon number 1-4.

The benzotriazole derivative includes benzotriazole, 4-methyl-benzotriazole, 5-methyl-benzotriazole, 4,7-dimethyl-benzotriazole, 5,6-dimethyl-benzotriazole.

The surface treatment method for carbon steel screws comprises the steps of:

-   (1) cleaning the surfaces of carbon steel screws so that the     impurities thereon are removed; -   (2) processing the carbon steel screws with a plurality of corrosion     inhibitors under 60-80° C.; -   (3) adding a silane and a fluoride-containing surfactant; baking the     screws under 120-150° C., whereby a thin layer of siloxane will be     formed on the surfaces of the screws; -   (4) immersing the screws in a baking formula and baking the screws     under 170-180° C., where the baking formula comprises:

polyethylene glycol of molecular weight 2000-10000 as an adhesive material.

The properties of the particles of metallic zinc, nickel and aluminum are changed by the silane so that they are easy to uniformly distributed in the polyethylene glycol solution.

The fluoride-containing surfactant effectively reduces the surface tension of the silane and thereof smoothens the coating.

The corrosion inhibitors are used to remove the impurities of the surface or after the process of zinc plating. The screws immersed in the mixture of the corrosion inhibitors are processed with a centrifugal and drying means to become carbon steel screws or zinc plated carbon steel screws.

The mixed-type additive can inhibit the adhesive material from being destroyed.

Thereby, the surfaces of the carbon steel screws can be plated with a layer of metallic zinc with a thickness of 7-8 microns through electrolysis.

Preferably, the associated baking formula comprises:

-   a. metallic zinc solution of concentration 5 grams per liter; -   b. metallic nickel solution of concentration 0.2 grams per liter; -   c. metallic aluminum solution of concentration 10 grams per liter; -   d. a fluoride-containing surfactant of concentration 0.2%; -   e. a plurality of corrosion inhibitors in a mixture of succinic     anhydride, n-butylamine, n-octylamine, n-decylamine and     n-dodecylamine; -   f. polyethylene glycol of concentration 30 grams per liter and of     molecular weight 2000-10000; and -   g. a mixed-type additive of concentration 50 ppm.

The associated surface structure produced by the present invention comprises a carbon steel screw, a surface protective layer over the screw produced by the associated baking formula, whose contents are described above.

The preferred embodiments processed by the surface treatment method for carbon steel screws embedded within anticorrosive wood are compared with the surfaces treated by the surface treatments of the prior art.

Experiment One:

Step 1: removing the rust and impurities on the surface of carbon steel screws by a mechanical means including cleansing and drying;

Step 2: immersing the carbon steel screws within the plurality of corrosion inhibitors under 60° C.˜80° C. to form a collection of treated carbon steel screws without chromium-6;

Step 3: adding the silane and the fluoride-containing surfactant and baking the solution at 120-150° C. to form a smooth layer of silicon oxide over the surfaces of the carbon steel screws; and

Step 4: baking the carbon steel screws in the baking finishing formula at 170-180° C. to from a protective layer over the surfaces; the baking finishing formula comprise metallic zinc solution of concentration 5 grams per liter, metallic nickel solution of concentration 0.2 grams per liter, metallic aluminum solution of concentration 10 grams per liter, a fluoride-containing surfactant of concentration 0.2%, polyethylene glycol of concentration 30 grams per liter and of molecular weight 2000-10000; and a mixed-type additive of concentration 50 ppm. The screws are tested over 90 days by AWPA E-12 94, and the result is shown in FIG. 1. The weight loss after the test is less then 0.2%.

Experiment Two:

Step 1: removing the rust and impurities on the surface of carbon steel screws by a mechanical means including cleansing and drying;

Step 2: coating the surface of the carbon steel screws with a metallic zinc layer of particle size 7-8 microns by electrolysis;

Step 3: immersing the carbon steel screws within the plurality of corrosion inhibitors under 60° C.˜80° C. to form a collection of treated carbon steel screws without chromium-6;

Step 4: adding the silane and the fluoride-containing surfactant and baking the solution at 120-150° C. to form a smooth layer of silicon oxide over the surfaces of the carbon steel screws; and

Step 5: baking the carbon steel screws in the baking finishing formula at 170-180° C. to from a protective layer over the surfaces; the baking finishing formula comprise metallic zinc solution of concentration 5 grams per liter, metallic nickel solution of concentration 0.2 grams per liter, metallic aluminum solution of concentration 10 grams per liter, a fluoride-containing surfactant of concentration 0.2%, polyethylene glycol of concentration 30 grams per liter and of molecular weight 2000-10000; and a mixed-type additive of concentration 50 ppm. The screws are tested over 90 days by AWPA E-12 94, and the result is shown in FIG. 2. The weight loss after the test is less then 0.1%.

An Experiment by a Traditional Method for Comparison:

Step 1: removing the rust and impurities on the surface of carbon steel screws by a mechanical means including cleansing and drying; coating the surface of the carbon steel screws with a metallic zinc layer of particle size 7-8 microns by electrolysis;

Step 2: treating the carbon steel screws with chromium-6;

Step 3: baking the screws at 170-180° C. to form a surface inactivated protective layer by the baking finishing formula comprising metallic zinc solution of concentration 5 grams per liter, metallic aluminum solution of concentration 10 grams per liter, polyethylene glycol of concentration 30 grams per liter (PEG 2000˜10000). The screws are tested over 90 days by AWPA E-12 94, and the result is shown in FIG. 3. The weight loss after the test is higher then 1%.

Therefore, the surface treatment method for carbon steel screws embedded within anticorrosive wood and the associated surface structure of the screws are realized by the baking finishing formula. The present invention is tested by AWPA E-12 94 and results in a loss of weight of 1%-0.2%, compared with a loss of 1% by a traditional method.

The present invention has the following advantages:

1. the smooth thin film formed on the zinc-plated surfaces of the carbon steel screws being superior to the traditional film of chromium-6 in anticorrosion;

2. the baking finishing formula of the present invention being environment-friendly; and

3. the surface treatment of screws of the present invention forming a smooth and fine protective layer over the surfaces which will be tightly attached to the substrate material, whereby the layer can sustain the friction caused when the screws are being used and the corrosion by the anticorrosive wood.

The present invention is thus described, and it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

1. A baking finishing formula for carbon steel screws, composing: a. metallic zinc solution of concentration 5-10 grams per liter and ion particle size 25-75 microns in diameter; b. metallic nickel solution of concentration 0.2-0.5 grams per liter and ion particle size 100-200 microns in diameter; c. metallic aluminum solution of concentration 10-20 grams per liter and ion particle size 15-25 microns in diameter; d. a fluoride-containing surfactant of concentration 0.2% and corresponding to polyethylene glycol; e. a plurality of corrosion inhibitors in a mixture of succinic anhydride, n-butylamine, n-octylamine, n-decylamine and n-dodecylamine; f. polyethylene glycol of concentration 30-50 grams per liter and of molecular weight 2000-10000; and g. a mixed-type additive of concentration 10-60 ppm.
 2. The baking finishing formula for carbon steel screws of claim 1 wherein said mixed-type additive is a benzotriazole derivative with the following molecular structure:

where groups R1, R2, R3 and R4 are selected from alkyls of carbon number 1-4.
 3. The baking finishing formula for carbon steel screws of claim 2 wherein said benzotriazole derivative is selected form one of Benzotriazole, 4-methyl-benzotriazole, 5-methyl-benzotriazole), 4,7-dimethyl-benzotriazole, and 5,6-dimethyl-benzotriazole.
 4. The baking finishing formula for carbon steel screws of claim 1 wherein said fluoride-containing surfactant is a product of 3M (Minnesota Mining and Manufacturing Co.) with a product number of FC-4430.
 5. The baking finishing formula for carbon steel screws of claim 1 wherein said plurality of corrosion inhibitors is a mixture of succinic anhydride, n-Butylamine, n-Octylamine, n-Decylamine and n-Dodecylamine.
 6. A surface treatment method for carbon steel screws using the baking finishing formula for carbon steel screws of claim 1, comprising the steps of: (1) cleaning the surfaces of carbon steel screws so that the impurities thereon are removed; (2) processing the carbon steel screws with a plurality of corrosion inhibitors under 60-80° C.; (3) adding a silane and a fluoride-containing surfactant; baking the screws under 120-150° C., whereby a thin layer of siloxane will be formed on the surfaces of the screws; and (4) immersing the screws in a baking formula and baking the screws under 170-180° C., said baking finishing formula comprising: (a) metallic zinc solution of concentration 5-10 grams per liter and ion particle size 25-75 microns in diameter; (b) metallic nickel solution of concentration 0.2-0.5 grams per liter and ion particle size 100-200 microns in diameter; (c) metallic aluminum solution of concentration 10-20 grams per liter and ion particle size 15-25 microns in diameter; (d) a fluoride-containing surfactant of concentration 0.2% and corresponding to polyethylene glycol; (e) a plurality of corrosion inhibitors in a mixture of succinic anhydride, n-butylamine, n-octylamine, n-decylamine and n-dodecylamine; (f) polyethylene glycol of concentration 30-50 grams per liter and of molecular weight 2000-10000; and (g) a mixed-type additive of concentration 10-60 ppm.
 7. The surface treatment method for carbon steel screws of claim 6 wherein the surfaces of said carbon steel screws are clean and the impurities thereon are removed.
 8. The surface treatment method for carbon steel screws of claim 7 wherein said baking finishing formula comprises: a. metallic zinc solution of concentration 5 grams per liter; b. metallic nickel solution of concentration 0.2 grams per liter; c. metallic aluminum solution of concentration 10 grams per liter; d. a fluoride-containing surfactant of concentration 0.2%; e. a plurality of corrosion inhibitors in a mixture of succinic anhydride, n-butylamine, n-octylamine, n-decylamine and n-dodecylamine; f. polyethylene glycol of concentration 30 grams per liter and of molecular weight 2000-10000; and g. a mixed-type additive of concentration 50 ppm.
 9. The surface treatment method for carbon steel screws of claim 6 wherein a layer of zinc of metallic zinc particles 7-8 microns formed on the surfaces of said carbon steel screws by electrolysis after said step
 1. 10. A surface structure of carbon steel screws treated by said baking finishing formula of claim 1, comprising: a screw made of carbon steels; and a protective layer over the surface of said screw made of a baking finishing formula comprising: (a) metallic zinc solution of concentration 5-10 grams per liter and ion particle size 25-75 microns in diameter; (b) metallic nickel solution of concentration 0.2-0.5 grams per liter and ion particle size 100-200 microns in diameter; (c) metallic aluminum solution of concentration 10-20 grams per liter and ion particle size 15-25 microns in diameter; (d) a fluoride-containing surfactant of concentration 0.2% and corresponding to polyethylene glycol; (e) a plurality of corrosion inhibitors in a mixture of succinic anhydride, n-Butylamine, n-Octylamine, n-Decylamine and n-Dodecylamine; (f) polyethylene glycol of concentration 30-50 grams per liter and of molecular weight 2000-10000; and (g) a mixed-type additive of concentration 10-60 ppm.
 11. The surface structure of carbon steel screws of claim 10 wherein said baking finishing formula comprises: a. metallic zinc solution of concentration 5 grams per liter; b. metallic nickel solution of concentration 0.2 grams per liter; c. metallic aluminum solution of concentration 10 grams per liter; d. a fluoride-containing surfactant of concentration 0.2%; e. a plurality of corrosion inhibitors in a mixture of succinic anhydride, n-butylamine, n-octylamine, n-decylamine and n-dodecylamine; f. polyethylene glycol of concentration 30 grams per liter and of molecular weight 2000-10000; and g. a mixed-type additive of concentration 50 ppm. 